Servicing Mission 3B - Another refurbishment for Hubble

Orbiting at a speed of about 27,200 km per hour, 570 km above the Earth, Hubble suffered from the progressive failure of several gyroscopes – responsible for keeping the observatory steady during observations – in 1999. Left unable to perform science operations until repairs were carried out, NASA split the third servicing mission in two separate flights: SM3A and SM3B.

Upon successful completion of SM3A - marked by the replacement of Hubble’s gyroscopes - in December of 1999, the fourth servicing mission to the Hubble Space Telescope was launched on 1 March 2002.

In preparation for this mission, the 7-astronaut Columbia crew (STS-109) underwent a training period that included extensive cross tuition and required that all astronauts received specific rehearsals tailored to their assigned tasks.

Led by Commander Scott D. Altman, the crew flew aboard the Columbia Space Shuttle to the space telescope and conducted a number of extra vehicular activities to upgrade the spacecraft. The almost-12-day mission featured five spacewalks and the installation of new science instruments.

Crucial to putting Hubble at the apex of its capabilities was the installation of a new scientific instrument - the Advanced Camera for Surveys (ACS) - containing advanced technology that far surpassed what had been available to the telescope to date.

The ACS replaced the Faint Object Camera and brought powerful new capabilities to Hubble. It is able to gather 10 times more data than the Wide Field and Planetary Camera 2 in the same span of time. With a wide field of view, high image quality and extraordinary sensitivity, Hubble’s ACS enhanced the spacecraft’s capabilities from visible to far ultraviolet. The ACS enabled to capture the most distant image of our Universe called the Hubble Deep Field, which has helped astronomers unveil the deepest and farthest mysteries of our Universe.

Although the principal task was the installation of the ACS, several other key upgrading activities were also conducted:

The 8-year old solar array panels were replaced with smaller rigid ones that produce 20 percent more power.

The outdated Power Control Unit was replaced. The PCU is used to distribute electricity from the solar arrays and batteries to other parts of the telescope. This combined with the new solar arrays led to a 30 percent power increase overall.

One of the four reaction wheel assemblies that make up Hubble’s pointing control system was also exchanged.

Another important upgrade was the installation of a new cooling system for the Near Infrared Camera and Multi-Object Spectrometer (NICMOS), which had been inoperable since 1999 after depleting its coolant. With this upgrade, Hubble regained its infrared vision.

After numerous refurbishing and maintenance tasks during this mission, astronauts left Hubble ready to achieve its full potential and to continue revolutionising modern astronomy by carrying out new observations and delivering unseen views of our Universe.